Best bang for wattage is a full spectrum that is focused in more of the red area. Think high pressure sodium colors for algae vs netal halide for corals. It may not be very noticeable since a lot of factors go into macroalgae growth from competition in main tank to nutrient levels in the water. From a physics perspective, a blue light takes twice as much energy to create the same photon as a red light, but the each photon (assuming it is bot reflected by the pigments) produces the same amount of energy from photosynthesis. Again, there are a lot of other variables to factor in here, but from a simplified physics perspective, you will get more par out a 1W warm white bulb than a 1W royal blue bulb. A few forums at reef central recommend a 2100K bulk.
Optimists say the glass is half full. Pessimists say the glass is half empty. Engineers say the glass is twice the size that it needs to be.